Commutator cap construction



C. A. ATWELL ETAL May 28, 1946.

COMMUTATOR CAP CONSTRUCTION Filed April I14. 1944 allllalapllllllINVENTORS Varenne/9 /7we// anal/Vorman MY/y.

BY 9 2 Z ATTORNEY Patented May 28, 1946 UNITED STATES PATENT OFFICECOMMUTATOR CAP CONSTRUCTION Application April 14, 1944, Serial No.530,960

(Cl. YY1- 321) 2 Claims.

Our invention relates to molded V-ring caps for motor commutatore; andin particular, our invention relates to a more suitable means for takingthe place of the string-bands or wrappings which have been commonlyutilized on the extending ends of insulating V-rings for approximatelyfour decades, or ever since there has been any occasion for retainingthese ends against centrifugal force. These string-bands have had anumber of objectionable features, being somewhat costly to apply,subject to breakage if but a single strand of the string is broken, andsomewhat difficult to coat with a smooth, glossy, insulatingpaint-surface so that it can be easily wiped off and will not so readilyaccumulate dirt which would impair the insulation creepage surface. Inthe case of a motor-flash, between one of the commutator-bars and themetal clamping V-ring under the insulating V-ring, a slight damage to astring-band allows all of it to come loose. Many corrective proposalshave been brought forward and tried out, during the course of the years,but in spite of its obvious disadvantages, the string-band has so farproven to be the most successful and acceptable bindingmeans for thefree end of the insulating V-rings, up until the time of our presentinvention.

The object of our present invention is to provide a novel method andmeans for retaining the free ends of insulating V-rings, utilizing arigid insulating cap which has suicient mechanical strength to resistcentrifugal forces, and which is slid on axially over the end of theinsulating V-ring, in substantial Contact with the large end thereof,after which, the space between the cap and the extended portion of theinsulating V-ring is substantially filled with a plastic heat-hardenableinsulating cement, which is iinally hardened by means of a suitableheatetreatment.

With the foregoing and other objects in View, our invention consists inthe combinations, systems, structures, parts, and methods hereinafterdescribed and claimed, and illustrated in the accompanying drawing,wherein Figure 1 is a fragmentary view of a portion of a motor embodyingour invention, on a slightly reduced scale, and

Fig. 2 is a considerably enlarged detail of the commutator cap assembly.

In Fig. l, we have shown our invention applied to a commutator-typedynamo-electric machine in the form of a direct-current railwaytractionmotor, comprising a statormember 3 and a rotormember 4, thelatter being mounted on a shaft 5 and carrying a commutator-assembly 6embodying our invention. The commutator-assembly is made up of a numberof copper commutator-bars 'l separated by mica or other insulating bars8, the two kinds of bars being of similar size and shape, except thatthe insulating bars are thinner and commonly project back aboutone-eighth of an inch behind the commutator-bars, as indicated by thenumeral 8, that is, the mica bars 8 are longer than the copper bars 1.The bars 'I and 8 are provided with V-grooves 9 in the ends thereof,said V-grooves having inclined, an inner, arch-binding surface II,usually at a angle, and an outer surface I 2, usually at a 3 angle, orsometimes a 6 angle.

The V-grooves 9 are insulatingly engaged by clamping V-rings I3 and I3',usually of steel, having conical surfaces inclined at the same angles asthe surfaces of the V-grooves. The insulating engagement is providedthrough the intermediary of insulating V-rings I4, preferably made ofsheet-mica of suieient thickness towithstand the maximum voltage whichis applied to the commutator-member.

At least the outer clamping V-ring I3', or the one at the end of themachine, has an outer conical surface I5 which extends out of theassociated V-groove 9, beyond the end of the commutator-bars l. Thecorresponding insulating V-ring I 4 likewise has an extended outerconical portion I6 which lits against the extended portion I5 of theclamping V-ring, and which preferably extends out substantially to thelarge end of the outer conical surface I5 of the clamping V-ringT I3. Itis this free or extended portion I6 of the insulating V-ring I4 whichwas formerly held down by a string-band.

The clamping-rings I3 and I3 are held in clamping-position by means of abolt I2! applied to the ring I3 so as to hold the inner conical surfaceI8 of each clamping-ring in arch-binding clamping-engagement with thecorresponding surface Il of the respective V-grooves.

The commutator-bars l are provided with armature-connections 20 whichcause the ccm-- mutator-bars to operate at such voltage as to involvethe danger of flashovers to ground, under operating conditions of themachine, particularly when the machine is utilized as a street-car orelectric-locomotive motor which is operated close to the ground, in wet,dirty weather. Such iiashovers may take the form of arcs from the freeends of one o1' more commutator-bars l, to any adjacent groundedsurface, such as the end of the associated clamping V-ring I3', or, asshown, we provide flashing-sectors 2I which are carried by thebearing-cartridge 22, between the brushhoider-supporting structures 25which support the brushholders 26 for carrying the brushes 2l which bearon the cylindrical surface of the commutator.

In accordance with our invention, the free extending ends I6 of theinsulating V-rings I4 are held down, and at the same time protectedagainst flashings, by means of a rigid insulating cap 3S, which ispreferably molded of layers of impreg nated asbestos-paper, so as toprovide a rigid structure of sufficient mechanical strength to re sistcentrifugal forces. Said cap 30 has a substantially cylindrical portion3| which extends over said extending portion I6 of the insulating V-ringI4. The cap also has a radial flange-pon tion 32 which extends over theend of the associated clamping V-ring I3.'. Preferably, thesubstantially cylindrical portion 3| of the cap 3D is of such diameterthat its inner surface is substantially in direct contact with theend-portion cr largest end of the extended portion I6 of the insulatingV-ring I4, or at least in contact in spots. or in certain motors, incase of variation in the diameter of the insulating V-rings in differentmotors.

In utilizing our invention, the cap 30 is slid on axially over theextended end I6 of the insulating V-ring i4. If the insulating V-ringend I6 is of too large a diameter, as by reason of a slight rougheningof the mica sheet-material or surface, its outer surface may be rstsandpapered slightly in order to admit of the application of the cap 3U.The inside of the cap or ring 30 is first smeared with cement, and thenthe cap is pushed in place, so that after it is in place, the spaceunderneath its cylindrical portion 3l, between the same and the inclinedor conical outer surface of the extended portion I6 of the insulating V-ring I4, is substantiatlly filled with plastic heathardenable insulatingcement, such as a polymerizing cement 33. This operation is preferablyperformed before the usual dipping and baking operation which is appliedto the armature 35 of the machine. The entire machine, or just therotor-member thereof, is then subjected to a suitable heat-treatingoperation, such as baking for several hours, which sets or hardens thecement 33 at the same time that it sets the dipping-compound with whichthe armature 35 is treated.

It will be obvious, from the foregoing description, that our inventionhas several advantages, among which may be mentioned the following:

(1) It is simple, thus differing markedly from many other elaborateschemes which have been suggested for avoiding some of the difficultiesof the string-bands.

(2) Our cap 3D provides increased creepagedistance to ground, because ofits end-flange 32 which extends downward over the end of the metalV-ring I3. This permits a more compact commutator-design, by making itpossible to use a shorter axial distance between the end of thecommutator and the end of the metal V-ring.

(3) It has ease of application. The labor of cementing the cap or ring30 in place requires much less time than the application f a stringband.

4) It is effective. The centrifugal force of the motor-revolution doesnot loosen the cap, as it often does the string-bands, because the capis all one solid piece. This makes it possible to successfully operatethe motor under modern conditions of high-speed street-car service.

(5) The outside of the cap provides a smoother surface than is providedby a string-band, even though the string-band is covered with a thickapplication of glossy paint, The surface of the cap can be painted witha smooth glossy finish of insulating paint, which can be kept clean veryeasily, and which provides a much better insulating creepage-surfacethan formerly.

(6) In case 0f motor-flash, the only possibility of damage to the capwill be a slightly damaged surface, but the flash will seldom burn thecap suiciently to necessitate its replacement. It may be smoothed withsandpaper and repainted and will be practically as good as new. On thecontrary, with the old string-band construction, a slight damage to astring-band allows all of it to come loose.

We claim as our invention:

l. A V-ring commutator-assembly of commutator-bars and, insulating barsseparating the commutator-bars, said bars having V-grooves in the endsthereof, insulating V-rings, clamping V -rings having a conical surfacetightly engaging a corresponding surface of the V -grooves, with theinsulating V-rings interposed in between, at least one of said clampingV--rings having an outer conical surface which extends out of theassociated Vg1'oove, beyond the end of the commutator-bars, the outerconical `portion of the corresponding insulating V-ring likewise havingan extended portion fitting against the extended portion of the clampingVring, a separately formed rigid insulating cap having sufficientrnechanical strength to resist centrifugal forces, said cap having asubstantially cylindrical portion extending over said extended portionof the insulating V-ring and further having an inte- ,eralflange-portion extending over the end of the associated clamping V-ring.whereby said flangeporticn mechanically stifens and strengthens saidcylindrical portion and electrically extends the insulation creepagesurface of said cylindrical portion radially inwardly along saidflangeportion, and a filling of a hard insulating cement substantiallyfilling the space between said. cylindrical portion and said extendedportion of the insulating V-ring, characterized by the extended portionof the insulating V-ring extending substantially out to the end of theclamping V-ring, and further characterized by the substantiallycylindrical portion of the cap being substantially in direct contactwith the end-portion of the extended portion of the insulating V-ring,whereby the cap and the intervening cement constitute the soleencompassing means around said extended portion of the insulating i/ringfor holding the latter against radial displacement due to centrifugalforce, and whereby the insulating V-ringr and the intervening cement andthe close t between the substantially cylindrical portion of the cap andthe end-portion of the extended portion of the insulating V-ringconstitute the sole means for holding the flangeportion of the capagainst axial displacement away from the end of the clamping vaine.

2. A commutator-type dynamo-electric ma chine characterized by having aV-ring commutator-assernbly of commutator-bars and insulating barsseparating the commutator-bars, said bars having V-grooves in the endsthereof, insulating V-rings, clamping V-rings having a conical surfacetightly engaging a corresponding surface of the V-grooves, with theinsulating V- rings interposed in between, at least one of said clampingV-rings having an outer conical surface which extends out of theassociated V-groove, beyond the end of the commutator-bars, the outerconical portion of the corresponding insulating V-ring likewise havingan extended portion fitting against the extended portion of the clampingV-ring, a separately formed rigid insulating cap` having sufficientmechanical strength to resist centrifugal forces, said cap having asubstantially cylindrical portion extending over said extended portionof the insulating V-ring and further having an integral flange-portionextending over the end of the associated clamping V-ring, whereby saidflange-portion mechanically stiens and strengthens said cylindricalportion and electrically extends the insulation creepage surface of saidcylindrical portionl radially inwardly along said flange-portion, alling of a hard insulating cement substantially filling the spacebetween said cylindrical portion and said extended portion of theinsulating V-ring, and armature-connections to said commutator-bars forcausing the same to operate at such voltage as to involve the danger offlashovers to ground, under operating conditions of the machine, exceptfor the presence of said cap, characterized by the extended portion ofthe insulating V-ring extending substantially out to the end of theclamping V-ring, and further characterized by the substantiallycylindrical portion of the cap being substantially in direct Contactwith. the end-portion of the extended portion of the insulating V-ring,whereby the cap and the intervening cernentbonstitute the soleencompassing means around said extended portion of the insulating V-ringfor holding the latter against radial displacement due to cen trifugalforce, and whereby the insulating V- ring and the intervening cement andthe close iit between the substantially cylindrical portion of the capand the end-portion of the extended portion of the insulating V-ringconstitute the sole means for holding the iiange-portion of the capagainst axial displacement away from the end of the clamping V-ring.

CLARENCE A. ATWELL. NORMAN H. WILLBY.

